This invention relates to an improved prosthetic heart valve with a padded stent. More particularly, the invention is concerned with a prosthetic heart valve comprising a stent having a smooth, non-abrasive outer layer adapted to avoid abrasion damage during normal function of the valve.
The early development of prosthetic heart valves is well documented in papers given at symposia in 1960 and in 1968, published in PROSTHETIC HEART VALVES, Lyman A. Brewer, III, Ed., Charles C. Thomas Publishing Co., Springfield, Ill. (1969), Second National Conference on Prosthetic Heart valves; PROSTHETIC VALVES FOR CARDIAC SURGERY, K. Alvin Merendino, Editor, Thomas Publishing Co., Springfield, Ill. (1961).
Lefrak and Starr recently surveyed the development of cardiac valve prostheses, E. A. Lefrak, and A. Starr, CARDIAC VALVE PROSTHESES, Appleton-Century-Krofts, New York, 1979 and the development of tissue heart valves has been comprehensively reviewed by Ionescu, Marian I., TISSUE HEART VALVES, Butterworths, Boston, 1979.
Great efforts have been expended in the development of tissue heart valve prostheses and in the development of supportive structures, or stents, for tissue valves. Representative of efforts to develop stents for tissue valves are the disclosures in the following U.S. Pat. Nos. 3,570,014, W. D. Hancock, Mar. 16, 1971; 3,714,671, William Sterling Edwards, et al, Feb. 6, 1973; 3,755,823, W. D. Hancock, Sept. 4, 1973: 3,983,581, William W. Angell, Oct. 5, 1976; 4,035,849, William W. Angell et al, July 19, 1977; 4,079,468, Domingo Santo Liotta, Mar. 21, 1978: 4,084,268, Marian I. Ionescu et al, Apr. 18, 1978; 4,106,129, Alain F. Carpentier, et al, Aug. 15, 1978; 4,172,295, Richard J. Batten, Oct. 30, 1979 and 4,192,020, Richard B. Davis, et al, Mar. 11, 1980. Other structures are also reported in the aforementioned treatises on heart valve developments.
Some of the earliest heart valve prostheses were flexible two-or three-cusp valves in which the cusps were constructed of various types of fabric. Some of these flexible leaflet valves had good flow characteristics but most failed early. The leaflets tore, separated from the annulus, or became rigid due to fibrous tissue ingrowth. From about 1960 into the 1970's, the trend was to mechanical valves. These ranged from the mechanically quite simple Starr-Edwards valve to the relatively sophisticated Bjork-Shiley valve and included a number of disc poppet valves. These mechanical valves generally dominated the market and are still very satisfactory for many applications. Tissue valves are still the preferred treatment where anti-coagulation therapy is not tolerated by the patient.
In 1962, Donald Ross and Sir Brian Barratt-Boyes, independently, were performing implantations of homograft tissue valves some of which were free graft implants and some were mounted on supporting stents. Fully clothed covered rigid stents were used in some of these homograft valves.
In 1965, Drs. Binet and Carpentier, and their associates, implanted a specially prepared porcine aortic valve xenograft. These porcine valves were sterilized and treated, e.g. with formaldehyde, and were commonly attached to a metal stent. Experience showed that these valves were of short life, largely because formaldehyde was used as the cross-linking agent. Formaldehyde was found to create reversible cross links in the tissue, thereby allowing early breakdown of the tissue. Dr. Carpentier, in about 1968, established the concept of the bioprosthesis by substantially eliminating antigenicity of the tissue, principally by changing the preservative from formaldehyde to glutaraldehyde. Glutaraldehyde has been shown to create cross links of a more permanent nature than those created by formaldehyde.
A number of porcine bioprostheses and specially designed stents for supporting these protheses resulted from the efforts of Warren Hancock et al. Generally, pig aortic valves are procured under clean conditions placed in a cold, balanced electrolyte solution, excess tissue is trimmed and the xenografts are immersed in 0.2% glutaraldehyde. The leaflets are held in their normal valving postion under pressure during the tanning process and each valve is sutured to a cloth covered stent by multiple sutures. A number of designs and stent constructions for the Hancock type valve are exemplified in the aforementioned U.S. Pat. Nos. 3,570,014 and 3,755,823. Stents for porcine valves were developed by a number of other workers also, see, e.g., U.S. Pat. Nos. 3,983,581; 4,035,849; 4,079,468 and 4,106,129.
Stents for supporting cusp valves of other tissue members, e.g. fascia lata and pericardium, have been developed by a number of workers, see, e.g., U.S. Pat. No. 3,714,671. Much of the pioneering work in this area of valve development was done by Dr. Marian I. Ionescu and his associates, see, e.g., Bartek, et al, FRAME-MOUNTED TISSUE HEART VALVES: TECHNIQUE OF CONSTRUCTION, Thorax, Volume 29, Pages 51-55, 1974; Ionescu, et al, HEART VALVE REPLACEMENT WITH IONESCU-SHILEY PERICARDIAL XENOGRAFT, Cardiology Digest, June, 1977; Ionescu, et al, HEART VALVE REPLACEMENT WITH IONESCU-SHILEY PERICARDICAL XENOGRAFT, The Journal of Thoracic and Cardiovascular Surgery, Volume 73, Pages 31-42, 1977; Tandon, et al, LONG-TERM HEMODYNAMIC EVALUATION OF AORTIC PERICARDIAL XENOGRAFT, British Heart Journal, Volume 40, Pages 602-607, 1978; Ionescu, et al, LONG-TERM CLINICAL AND HEMODYNAMIC EVALUATION OF THE IONESCU-SHILEY PERICARDIAL XENOGRAFT HEART VALVE, Thoraxchirurgie, volume 25, Pages 250-258, 1978; Ionescu, et al, LONG-TERM SEQUENTIAL HEMODYNAMIC EVALUATION OF RIGHT VENTRICULAR OUTFLOW TRACT RECONSTRUCTION USING A VALVE MECHANISM, The Annals of Thoracic Surgery, 27, 425-434, 1979; and Ionescu, Editor, TISSUE HEART VALVES, Butterworths, 1979.
A number of improvements in the basic Ionescu tissue heart valve have been made. For example, a tissue heart valve has been developed which has a cloth-covered stent of special construction, in which the outflow annulus diameter of the valve is defined and limited by the positioning of a coaptation stitch on the inside of the supporting legs of the stent, as has been the practice since the early development of the Ionescu type tissue heart valve. Another improvement in the method for aligning the tissue of the cusps of the Ionescu type heart valve is described in U.S. Pat. No. 4,172,295 which also disclosed the coaptation stitch inside the stent legs.
A heart valve with a removable cusp protector band is disclosed in U.S. Pat. No. 4,364,126.
A potential problem remains in the heart valves described in the above references, namely, that stress is concentrated in the tissue in some areas where sharp bending of the tissue around the stent occurs. The stress tends to be highest at points of maximum curvature such as around the tips of the stent legs because of the pinching of the tissue leaflets together inside and above the tip of the stent leg. A solution to this problem is disclosed in U.S. patent application Ser. No. 327,081, filed Dec. 3, 1981. U.S. Pat. No. 4,441,216, issued Apr. 10, 1984).
A further problem of prior art prosthetic heart valves is the abrasion caused by the rubbing of a tissue valve leaflet over a fabric covered stent. This problem is substantially solved by the present invention.